Throughout the present description and the subsequent claims, with the term “reader of coded information” it is intended to indicate any device capable of acquiring information related to an object (for example, distance, volume, size or identifying data thereof) by acquiring and processing a light signal diffused or reflected from the same object. With the term: “coded information” it is intended to indicate the whole data contained in an optical code. With the term: “optical code” it is intended to indicate any graphical representation having the function of containing coded information. A particular example of optical code consists of linear or two-dimensional codes, wherein the information is codified by means of appropriate combinations of elements having a predetermined shape, for example squares, rectangles or hexagons, of dark colour (normally black) separated by clear elements (spaces, normally white), such as bar codes, stacked codes and two-dimensional codes in general, colour codes etc. The term “optical code” moreover comprises, more in general, also other graphical forms with information coding function, including printed characters (letters, numbers, etc.) and particular patterns (such as for example stamps, logos, signatures, fingerprints etc.). The term “optical code” moreover comprises graphical representations which can be detected not only in the visible light field but also in the entire range of wavelengths between the infrared and the ultraviolet.
Only for exemplificative purpose and in order to make the following description clearer, explicit reference will often be made hereinafter to a bar code reader (linear reader); of course, a person skilled in the art will recognize that what said is applicable to readers of different type, such as for example “stacked”-type two-dimensional optical code readers.
Furthermore, reference will often be made to the “light diffused” from a support containing an optical code, generally intending with this expression the light coming from the illuminated optical code, and therefore also the “light reflected” directly by the illuminated optical code.
As it is known, a laser scanner device for reading an optical code typically comprises, in the simplest configuration thereof, an emission source of a laser light beam, a scanning optical element of said laser light beam on a support containing the optical code to be read, a collecting system of the light diffused by the illuminated optical code and a photoreceiver which is sensitive to the light diffused by the illuminated optical code in order to generate a photoelectric signal whose time modulation represents the information contained in the optical code.
The prior art scanning devices are typically of rotating or oscillating type, depending on the type of motion which the scanning optical element is subjected to.
With particular reference to the scanning devices of oscillating type, those known in the prior art are generally based on optical systems of retroreflective or semiretroreflective type. Such devices provide in particular for the use of an oscillating mirror which acts both as scanning optical element of the laser light beam on the optical code and as collecting element of the light diffused by the illuminated optical code, such light being then directed towards the photoreceiver.
Actually, scanning devices of oscillating type are also known, wherein the scanning of the laser light beam is obtained by directly placing in oscillation the emission source and/or the photoreceiver, and the focusing and collecting lenses associated therewith. Such devices, however, have the drawback of requiring movable connections in order to allow controlling the laser source and/or extracting the photoelectric signal from the photoreceiver.
Coming back to the scanning devices which use an oscillating mirror, such mirror is generally put into motion by a brushless or galvanometric electromagnetic motor, or by a bimorph resonant motor, as for example described in U.S. Pat. No. 4,387,297. It is also known to move the oscillating mirror by means of a resonant motor which uses a planar spring in mylar or other non-metallic material, such as for example described in U.S. Pat. No. 5,917,173, U.S. Pat. No. 5,900,617 and U.S. Pat. No. 5,367,151.
The scanning devices of oscillating and retroreflective type further comprise, typically, in addition to the mirror for scanning and collecting the light, a deflecting mirror for deflecting outwards the laser beam emitted by the emission source and a further collecting and deflecting mirror for deflecting towards the photoreceiver the light diffused by the illuminated optical code. The Applicant observes that the use of a deflecting mirror of the light emitted by the emission source and of a deflecting mirror towards the photoreceiver of the light diffused by the illuminated optical code requires making two additional mirror-like elements (in addition to the mirror for scanning and collecting the light), i.e. elements having surfaces with metal treatment which require a costly and hard-to-control deposition process. Moreover, the deflecting mirror of the light emitted by the emission source constitutes an obstruction in the optical collection path of the light diffused by the illuminated code. All of this implies an increase of the manufacturing costs of this additional mirror-like element and a complication of the structure configuration and of the layout of the device, due to the need to particularly take care of the positioning of the two separate mirror-like elements. Such a complication becomes even greater the more one wishes to miniaturise the device.
The Applicant further observes that, in most of the currently known solutions, a metal or plastic frame which houses all of the mechanical and optical components is provided. The structure of such frame is particularly complex and its manufacturing requires very accurate and expensive moulds, in order to ensure the correct mutual positioning of the components.
The technical problem at the basis of the present invention is that of identifying a structural and layout configuration for a scanning device of oscillating type which allows reducing to a minimum or even eliminating the size of the required mirror-like surface, thus saving on the manufacturing cost of the device, and which allows miniaturising the device as much as possible, simplifying as much as possible the optical collection path.